Non-invasive Monitoring of Hemodynamic Changes During Hemodialysis by the Use of a Newly Developed Admittance Cardiograph

Changes in cardiac output with hemodialysis relate to net volume balance and to inferior vena cava ultrasound collapsibility in critically ill patients

Cardiac output may increase after volume administration with relative intravascular volume depletion, or after ultrafiltration (UF) with relative intravascular volume overload. Assessing relative intravascular volume using respiratory/ventilatory changes in inferior vena cava (IVC) diameters may guide volume management to optimize cardiac output in critically ill patients requiring hemodialysis (HD) and/or UF.We retrospectively studied 22 critically ill patients having relative intravascular volume assessed by IVC Collapsibility Index (IVC CI) = (IVCmax-IVCmin)/IVCmax*100%, within 24 h of cardiac output measurement, during 37 intermittent and 21 continuous HD encounters. Cardiac output increase >10% was considered significant. Net volume changes between cardiac outputs were estimated from "isonatremic volume equivalent" (0.9% saline) gains and losses.Cardiac output increased >10% in 15 of 42 encounters with IVC CI <20% after net volume removal, and in 1 of 16 encounters with IVC CI ≥20% after net volume administration (p = 0.0136). All intermittent and continuous HD encounters resulted in intradialytic hypotension. Net volume changes between cardiac output measurements were significantly less (median +1.0 mL/kg) with intractable hypotension or vasopressor initiation, and net volume removal was larger (median -22.9 mL/kg) with less severe intradialytic hypotension (p < 0.001). Cardiac output increased >10% more frequently with least severe intradialytic hypotension and decreased with most severe intradialytic hypotension (p = 0.047).In summary, cardiac output may increase with net volume removal by ultrafiltration in some critically ill patients with relative intravascular volume overload assessed by IVC collapsibility. Severe intradialytic hypotension may limit volume removal with ultrafiltration, rather than larger volume removal causing severe intradialytic hypotension.

Long-term antihypertensive effects of aliskiren, a direct renin inhibitor, in chronic hemodialysis patients

The renin-angiotensin-aldosterone system is not necessarily suppressed in end-stage renal disease patients undergoing dialysis. Of all the inhibitors of this system, the clinical efficacy of the renin inhibitor, aliskiren, has not been well demonstrated in dialysis patients. We evaluated the antihypertensive effect of aliskiren, administered as a single daily dose of 150 mg for 24 weeks, in 23 chronic hemodialysis patients (age 65 ± 12 years, 15 men and eight women) with blood pressure ≥140/90 mm Hg, and assessed the factors relating to blood pressure reduction. At 4 weeks, the average systolic blood pressure before the dialysis session was insignificantly reduced from 163 ± 10 mm Hg to 160 ± 15 mm Hg, while it was significantly lowered at 12 (154 ± 13 mm Hg) and 24 weeks (155 ± 10 mm Hg), although the pulse rate was not significantly altered. Serum K increased at 24 weeks from 4.9 ± 0.6 mEq/L to 5.2 ± 0.8 mEq/L. Only 10 out of 23 patients showed systolic blood pressure reduction by ≥10 mm Hg. Naturally, plasma renin immunoreactivity increased, while plasma renin activity, along with angiotensin II and aldosterone levels decreased. Basal levels of the components of the renin-angiotensin-aldosterone system were not significantly different in patients showing systolic blood pressure reduction by ≥10 mm Hg (n = 10) vs. those with <10 mm Hg changes (n = 13). The reduction in systolic blood pressure in all 23 patients taken as a whole correlated with changes in plasma renin activity (r = -0.432, P < 0.05) and angiotensin II (r = 0.467, P < 0.05). In chronic hemodialysis patients, aliskiren modestly lowers blood pressure over the long term, although the antihypertensive effect seems dependent on the changes, but not on the basal levels of plasma renin activity and angiotensin II.

Frequency spectrum analysis of finger photoplethysmographic waveform variability during haemodialysis

This study investigates the peripheral circulatory and autonomic response to volume withdrawal in haemodialysis based on spectral analysis of photoplethysmographic waveform variability (PPGV). Frequency spectrum analysis was performed on the baseline and pulse amplitude variabilities of the finger infrared photoplethysmographic (PPG) waveform and on heart rate variability extracted from the ECG signal collected from 18 kidney failure patients undergoing haemodialysis. Spectral powers were calculated from the low frequency (LF, 0.04-0.145 Hz) and high frequency (HF, 0.145-0.45 Hz) bands. In eight stable fluid overloaded patients (fluid removal of >2 L) not on alpha blockers, progressive reduction in relative blood volume during haemodialysis resulted in significant increase in LF and HF powers of PPG baseline and amplitude variability (P < 0.01), when expressed in mean-scaled units. The augmentation of LF powers in PPGV during haemodialysis may indicate the recovery and possibly further enhancement of peripheral sympathetic vascular modulation subsequent to volume unloading, whilst the increase in respiratory HF power in PPGV is most likely a sign of preload reduction. Spectral analysis of finger PPGV may provide valuable information on the autonomic vascular response to blood volume reduction in haemodialysis, and can be potentially utilized as a non-invasive tool for assessing peripheral circulatory control during routine dialysis procedure.

Changes in the spectral powers of finger photoplethysmographic waveform variability in hemodialysis patients

This paper reports changes in the spectral powers of finger photoplethysmographic waveform variability (PPGV) following hemodialysis compared to pre-dialysis. The results are based on data collected from 12 hemodynamically stable patients having regular hemodialysis thrice weekly. Six minutes of continuous electrocardiogram (ECG) and finger infra-red photoplethysmographic (PPG) signals were collected at pre-dialysis and at end of dialysis. A four minute artefact free segment was selected and baseline and amplitude variabilities were derived from PPG waveform. Heart rate variability was derived from ECG R-R interval. Frequency spectrum analysis was then applied to these variability signals. The spectral powers were then calculated from low frequency (LF), mid frequency (MF) and high frequency (HF) bands. The results indicate that LF (p=0.01) and MF (p=0.02) powers of baseline PPGV (expressed in mean-scaled units) and LF (p=0.006), MF (p=0.003) and HF (p=0.017) powers of amplitude PPGV (expressed in mean-scaled units) showed a significant increase at the end of dialysis compared to pre-dialysis. HRV spectral measures did not show any significant change. The increase in LF and MF powers in PPGV may suggest the recovery and further enhancement of peripheral sympathetic vascular modulation as a result of volume unloading in initially hypervolemic dialysis patients, at the same time the increase in respiratory HF power in PPGV may indicate preload reduction.

Physiological responses to workload change. A test/retest examination

The purpose of this study is to examine the test/retest consistency of physiological responses induced by mental tasks. Fifteen healthy male university students were recruited as participants. They were instructed to perform a 5-min Multi-Attribute Task Battery (MATB) trial three times successively. The task difficulty level of the tracking task of the second trial was set as medium (M). The first one was set as more difficult (H) and the last trial was easiest (L). The difficulty levels of the other two tasks (resource management and system monitoring) of the MATB were identical for all three trials. The participants repeated this procedure on three different days separated by at least a 1-day interval. The order of the tasks was the same for all repeated trials, i.e., H-M-L. Tissue blood volume from the tip of the nose using a laser Doppler blood flow meter, skin potential level (SPL), ECG from three leads on the chest, systolic time intervals (pre-ejection period, left ventricular ejection time), and hemodynamic parameters (stroke volume, cardiac output) were recorded during the task trials and before and after 5-min resting periods. The participants reported their subjective workload via NASA-TLX after each task trial. Autonomic nervous system parameters derived from the above-mentioned signals, subjective workload scores, and performance indices of MATB were analyzed, and test/retest reliability was investigated. The results showed that a significant test/retest correlation was obtained for SPL for more participants than in the other parameters, although there were large individual differences.

Noninvasive Measurement of Cardiac Output in Hemodialysis Patients by Task Force Monitor: A Comparison with the Transonic System

Cardiovascular disease is the leading cause of morbidity and mortality in maintenance hemodialysis (MHD) patients. The Transonic (TRS; Transonic Systems, Ithaca, NY) device is frequently used for determination of cardiac output (CO) by an indicator dilution technique. The Task Force Monitor (TFM; CN Systems, Graz, Austria) has gained attention as noninvasive tool for continuous beat-to-beat assessment of cardiovascular variables, including CO by impedance cardiography. Despite its use in cardiology and intensive care settings, the TFM has yet not been validated in dialysis patients. This study compares CO measurements in 12 MHD patients by TFM and TRS. Bland-Altman and regression analysis were used. CO was measured simultaneously by TRS and TFM. Average CO was 5.4 L/min by TRS and 5.0 L/min by TFM, respectively. Bland-Altman analysis revealed no significant systematic differences between the two methods (mean difference: 0.4 L/min; SD: 0.6; p > 0.05). Linear regression analysis showed significant correlation between both techniques (r = 0.802, p = 0.002). The SD of mean individual CO values was 1.1 L/min with TRS and 0.8 L/min with TFM, respectively.CO measured by TFM and TRS does not differ significantly, thus making the TFM an attractive noninvasive tool for the continuous beat-to-beat assessment of CO in MHD patients.